Fix snapshots from Downloads being deleted by last_n.

chrome/browser/android/offline_pages/request_coordinator_factory.h

Index: chrome/browser/android/offline_pages/request_coordinator_factory.h
diff --git a/chrome/browser/android/offline_pages/request_coordinator_factory.h b/chrome/browser/android/offline_pages/request_coordinator_factory.h
index 7e4751dfaba9c1af41c816639b7e5a148c5c9e66..af9fdeea8ef5159e2a88b73937d5fee162ffd735 100644
--- a/chrome/browser/android/offline_pages/request_coordinator_factory.h
+++ b/chrome/browser/android/offline_pages/request_coordinator_factory.h
@@ -27,6 +27,7 @@ class RequestCoordinatorFactory : public BrowserContextKeyedServiceFactory {
 
  private:
   friend struct base::DefaultSingletonTraits<RequestCoordinatorFactory>;
+  friend class RecentTabHelperTest;
 
   RequestCoordinatorFactory();
   ~RequestCoordinatorFactory() override {}
@@ -34,6 +35,11 @@ class RequestCoordinatorFactory : public BrowserContextKeyedServiceFactory {
   KeyedService* BuildServiceInstanceFor(
       content::BrowserContext* context) const override;
 
+  // Used to always return nullptr instances while running tests.
+  void ReturnNullptrForTesting(bool enabled) { always_nullptr_ = enabled; }

[fgorski, 2016/12/13 17:17:38]

I don't think changing anything about request coordinator should be necessary
here.

Did you try using: SetTestingFactoryAndUse
And passing in a method that returns nullptr?

As an alternative you can use this:
https://cs.chromium.org/chromium/src/chrome/browser/android/offline_pages/tes...
in your test. This method was build for what you are trying to do.
Example usage is in offline_page_utils_unittest.cc
https://cs.chromium.org/chromium/src/chrome/browser/android/offline_pages/off...

[carlosk, 2016/12/13 20:04:20]

Done. Thanks for pointing it out. I did not know about SetTestingFactoryAndUse.

+
+  bool always_nullptr_ = false;
+
   DISALLOW_COPY_AND_ASSIGN(RequestCoordinatorFactory);
 };